The more prevalent construction for freight railcars in the U.S.A. includes what are known as "three piece" trucks. Trucks are wheeled vehicles that ride on tracks and two such trucks are normally used beneath the car body, one truck at each end. The "three piece" terminology refers to two side frames, that are positioned to parallel the wheels and rails, and a single bolster that is transverse to and spans the distance between the side frames. Railcar trucks must be strong enough to support both the car structure and its contents, particularly the bolsters on which the carbody is directly supported and do so in a severe operating environment that magnifies the static loading by a factor of 3 or greater. Most usually the side frames and bolsters are manufactured of cast steel. Thus the trucks themselves contribute a substantial part of the total weight placed on the rails. The latter is regulated by the rail line owners who are concerned with the safety and conditions of the track. Thus the maximum quantity of product that a shipper may place in a railcar will be affected by the weight of the carbody, its contents, and the trucks. Hence any weight reduction that may be made in the truck components will be available to increase the carrying capacity of the car. Weight reduction of the bolsters has heretofore been disfavored and regarded as particularly difficult as the bolster flexes when supporting the carbody between the two side frames and is known to therefore be subject to fatigue brought about by load cycling.